Single nucleotide polymorphisms of pattern recognition receptors and chronic periodontitis.

BACKGROUND AND OBJECTIVE: Periodontitis is a multifactorial disease influenced partly by genetics. Activation of pattern recognition receptors (PRRs) can lead to the up-regulation of inflammatory pathways, resulting in periodontal tissue destruction. Hence, functional polymorphisms located in PRRs can explain differences in host susceptibility to periodontitis. This study investigated single nucleotide polymorphisms of PRRs including toll-like receptor (TLR)2 (G2408A), TLR4 (A896G), TLR9 (T1486C), TLR9 (T1237C) and CD14 (C260T) in patients with chronic periodontitis and in periodontally healthy subjects. METHODS: One-hundred and fourteen patients with chronic periodontitis and 77 periodontally healthy subjects were genotyped using TaqMan® allelic discrimination assays. Fisher's exact test and chi-square analyses were performed to compare genotype and allele frequencies. RESULTS: The frequency of subjects with the CC genotype of CD14 (C260T) (24.6% in the chronic periodontitis group vs. 13% in the periodontally healthy group) and those expressing the T allele of CD14 (C260T) (CT and TT) (75.4% in the chronic periodontitis group vs. 87% in the periodontally healthy group) was statistically different among groups (p = 0.04). Homozygocity for the C allele of the CD14 (C260T) polymorphism (CC) was associated with a two--fold increased susceptibility to periodontitis (p = 0.04; odds ratio, 2.49; 95% confidence interval, 1.06-6.26). Individuals with the CC genotype of TLR9 (T1486C) (14.9% in the chronic periodontitis group vs. 28.6% in the periodontally healthy group) and those expressing the T allele of TLR9 (T1486C) (CT and TT) (85.1% in the chronic periodontitis group vs. 71.4% in the periodontally healthy group) were also significantly differently distributed between groups without adjustment (p = 0.03). Further analysis of nonsmokers revealed a significant difference in the distribution of genotypes between groups for TLR9 (T1486C; p = 0.017) and CD14 (C260T; p = 0.03), polymorphisms again without adjustment. CONCLUSION: The CC genotype of CD14 (C260T) is related to susceptibility to chronic periodontitis in Caucasians. In addition, differences observed in the distribution of TLR9 (T1486C) genotypes between groups warrant further investigation.

Recombinant expression and partial characterization of the human formyl peptide receptor.

FMLP-receptor DNA was expressed in Escherichia coli. The expressed product could specifically bind FMLP. This is the first-reported expression of a functional FMLP receptor in Escherichia coli. We confirm that receptor glycosylation is not essential for ligand binding. A deletion mutant did not bind FMLP, suggesting that the deleted portion plays a role in ligand binding.

Chemotactic-like receptors and Abeta peptide induced responses in Alzheimer's disease.

Evidence suggests that beta-amyloid (Abeta) has chemokine-like properties and may act through formyl chemotactic receptors (FPR) to induce pathophysiologically important functional changes in Alzheimer's disease (AD) microglia. We have shown that Abeta 1-42, fibrillar Abeta 1-40, and Abeta 25-35 potentiate the release of interleukin-1beta (IL-1beta) from LPS activated human THP-1 monocytes [26] and LPS primed rat microglia. Moreover, Abeta-stimulated IL-1beta secretion seems to be receptor mediated because it is calcium dependent and requires activation of specific G-proteins [27]. Thus, we have evaluated the ability of Abeta 1-42 to mimic formyl chemotactic peptides in stimulating IL-1beta release from THP-1 monocytes. Several of the formyl chemotactic peptides and Abeta 1-42 significantly enhanced IL-1beta production in THP-1 monocytes. In contrast, a formyl chemotactic receptor antagonist inhibited Abeta 1-42-induced IL-1beta release from both human THP-1 monocytes and primary rat microglia. Further, primary rat microglia grown in culture expressed FPR as demonstrated by immunocytochemistry. Given the multiple pathophysiologic roles IL-1beta may play in AD, agents that block Abeta interactions with formyl chemotactic receptors on microglia might be important antiinflammatory therapeutic targets.

Expression and purification of recombinant human N-formyl-L-leucyl-L-phenylalanine (FMLP) receptor: generation of polyclonal antibody against FMLP receptor.

The recombinant formyl peptide receptor has been successfully expressed and purified, utilizing an Escherichia coli expression system. Purification of formyl peptide receptor was performed using gel filtration chromatography and affinity chromatography, and the purified protein migrated at an apparent molecular mass of 36,000 Da. The purified recombinant receptor retained functional activity as determined by a ligand binding assay. The yield of the recombinant purified receptor was approximately 1 mg/2 L of culture, and the binding activity was determined to be approximately 8 nM, which suggests the conclusion that glycosylation does not affect significantly ligand binding of the N-formyl-L-leucyl-L-phenylalanine (FMLP) receptor molecule. The recombinant receptor protein yield was found to be significantly higher than that obtained from neutrophils. The purified recombinant receptor was then utilized to generate antibody against the same. The reaction of the antibody against recombinant formylpeptide receptor and against native formylpeptide receptor on neutrophils was confirmed by western blot analysis and flow cytometric analysis, respectively. The antibody was also used successfully to detect recombinant formylpeptide receptor expression on transfected 293 cells. These results describe for the first time the expression, purification, and characterization of recombinant FMLP receptor with ligand binding activity and the generation of polyclonal antibody against the same. This work also provides a foundation for future biophysical studies of the FMLP receptor molecule, which have not been possible until now.

Isolation and characterization of a human neutrophil aggregation defective mutant of Fusobacterium nucleatum.

Fusobacterium nucleatum is known to adhere to human polymorphonuclear neutrophils (PMNs) and cause them to aggregate. In this study, we isolated a spontaneously occurring aggregation defective (AGG(-)) mutant and this mutant will be used for future study of the interactions between this bacterium and human PMN. Genomic DNA fingerprinting by random-primed polymerase chain reaction method revealed a difference between the parent strain and the AGG(-) mutant. This mutant also showed an altered phenotype in both microbicidal and phagocytic assays, suggesting that the bacterial factor involved in the aggregation may also be very important for the phagocytosis and, subsequently, the killing by human PMNs. Further study of this mutant may help to clarify the molecular mechanisms of the interaction between this pathogen and human PMNs.

Serum cotinine levels, smoking, and periodontal attachment loss.

Cigarette smoking and tobacco use have been the subjects of numerous studies for many years. Smoking has also been associated with periodontal disease. However, no relationship between a reliable biochemical marker and increased severity of the periodontal condition has yet been described. It was thus the aim of this study to apply the measurement of cotinine, the major metabolite of nicotine, as a quantitative method to assess levels of smoking, and to correlate serum levels of cotinine with severity of periodontal disease. The degree of association between smoking and periodontal attachment loss was investigated in a study including 79 patients 25 to 64 years old suffering from periodontitis. Patients were examined and the following parameters recorded: Gingival Assessment (GA), Probing Pocket Depth (PPD), Clinical Attachment Level (CAL), and Bone Crest Height (BCH). In addition, self-reported histories of tobacco use as well as blood samples for quantitative analysis of serum levels of cotinine were taken. The serum samples were analyzed for cotinine content by means of a competitive-inhibition ELISA technique. The differences in mean cotinine levels were statistically significant (p = 0.0001) between smokers and non-smokers, showing no overlap between the groups. Severity of periodontal attachment loss was positively correlated with serum levels of cotinine for both measures of periodontal disease (CAL p = 0.005; BCH p = 0.008). Results from the present study indicate that serum cotinine levels used as a biochemical marker of smoking status are correlated with severity of periodontal attachment loss.

Single nucleotide polymorphisms of the N-formyl peptide receptor in localized juvenile periodontitis.

BACKGROUND: Neutrophils from patients with localized juvenile periodontitis (LJP) exhibit decreased binding and responsiveness to various chemotactic agents, including N-formyl-1-methionyl-1-leucyl-1-phenylalanine (FMLP). This altered reaction of neutrophils is thought to account in part for the increased susceptibility of LJP patients to infections by periodontal organisms. Receptors for FMLP are involved in the activation and the subsequent response to certain chemotactic stimuli. METHODS: In order to determine if this decreased response is due to a genetic variation in the receptor, we directly compared DNA encoding the FMLP receptor from controls matched for gender and race and LJP patients by single-strand conformation polymorphism analysis (SSCP). RESULTS: Using this technique, we observed a characteristic SSCP pattern in 29 out of 30 patient samples in the FMLP receptor DNA. This pattern differed from those obtained from the 20 control subjects as well as 31 patients with adult periodontitis. DNA sequencing of 30 patients indicated single nucleotide polymorphisms (SNPs) in the FMLP receptor DNA from the LJP patients when compared to 20 controls (P = 0.0005). Two single nucleotide base alterations were consistently seen: either a thymine to cytosine substitution at base 329 in 17 LJP patients or a cytosine to guanine substitution at base 378 in 5 LJP patients. A combination of both alterations were seen in 7 LJP patients. Both alterations resulted in amino acid changes in the second intracellular loop of the receptor, specifically phenylalanine to serine at residue 110 and cysteine to tryptophan at residue 126. This region of the FMLP receptor has recently been shown to play a role in ligand binding and G-protein activation. CONCLUSIONS: This study suggests that a molecular alteration in the second intracellular loop of the FMLP receptor molecules in LP patients may play a role in the decreased chemotactic activity reported for some LJP patients.

Periodontal infections contribute to elevated systemic C-reactive protein level.

BACKGROUND: Periodontitis is a local inflammatory process mediating destruction of periodontal tissues triggered by bacterial insult. However, this disease is also characterized by systemic inflammatory host responses that may contribute, in part, to the recently reported higher risk for cardiovascular disease (CVD) among patients with periodontitis. Moderate elevation of C-reactive protein (CRP) has been found to be a predictor of increased risk for CVD. Elevated CRP levels in periodontal patients have been reported by several groups. In this study, we examined whether CRP plasma levels are increased in periodontitis and if there is a relation to severity of periodontal disease and to the periodontal microflora. METHODS: CRP serum levels were assessed using radial immunodiffusion assay in 174 subjects, 59 with moderate mean clinical attachment loss (AL) (2.39+/-0.29 mm) and 50 with high AL (3.79+/-0.86 mm) as compared to 65 periodontally healthy controls (AL, 1.74+/-0.18 mm). Clinical attachment loss, probing depths, and percentage of periodontal pocket sites > or =5 mm were measured. The presence of periodontal pathogens Porphyromonas gingivalis (P.g.), Prevotella intermedia (P.i.), Campylobacter recta (C.r.), and Bacteroides forsythus (B.f.) in subgingival plaque samples was measured by immunofluorescence microscopy. RESULTS: Statistically significant increases in CRP levels were observed in subjects with periodontal disease when compared to healthy controls (P= 0.036). Subjects with high levels of mean clinical attachment loss had significantly higher mean CRP levels (4.06+/-5.55 mg/l) than controls (1.70+/-1.91 mg/l), P= 0.011. The CRP levels were adjusted for factors known to be associated with elevated CRP, including age, smoking, body mass index (BMI), triglycerides, and cholesterol. Age and BMI were found to be significant covariates. The reported range for CRP as a risk factor for CVD, peripheral vascular diseases, or stroke is 1.34 mg/l to 6.45 mg/l and the mean of this range is 3 mg/l. The percentage of subjects with elevated levels of CRP > or = 3 mm was significantly higher in the high clinical AL group (38%; 95% Cl: 26.7%, 49.3%) when compared to the control group (16.9%; 95% CI: 9.25%, 24.5%), P= 0.011. The presence of periodontal pathogens P.g., P.i., C.r., and B.f. in subgingival samples was positively associated with elevated CRP levels (P= 0.029). CONCLUSIONS: The extent of increase in CRP levels in periodontitis patients depends on the severity of the disease after adjusting for age, smoking, body mass index, triglycerides, and cholesterol. Also, there are elevated levels of CRP associated with infection with subgingival organisms often associated with periodontal disease, including P.g., P.i., C.r., and B.f. Recent investigations emphasized the role of moderate elevated CRP plasma levels as a risk factor for CVD. The positive correlation between CRP and periodontal disease might be a possible underlying pathway in the association between periodontal disease and the observed higher risk for CVD in these patients.

Immunochemical characterization of the formyl peptide receptor moieties on human neutrophils.

The neutrophil (PMN) receptor for formylated peptides such as N-formyl-l-methionyl-l-leucyl-l-phenylalanine (FMLP) is involved in binding and subsequent response to certain chemotactic stimuli. The receptor on human PMN has been reported to consist of several glycoprotein components, ranging in size from 43-94 kDa. Furthermore, FMLP receptors on human PMN have been shown to contain both high and low affinity states. In this study, the receptor was purified by subjecting solubilized PMN plasma membrane components to FMLP-affinity chromatography, and was found to be comprised of four components, one of 68 kDa, and the others of 94, 48, and approximately 40 kDa. Only the 68, the 94, and the approximately 40 kDa components specifically bound a radioiodinated FMLP analogue. To further characterize these components, a battery of monoclonal antibodies reactive against the FMLP receptor was prepared. Seven monoclonal antibodies were selected on the basis of their reactivity with the 68 kDa receptor component. Some of these antibodies also cross-react with the 48 kDa component, suggesting that the 68 and the 48 kDa receptor moieties are immunologically related. These antibodies reacted with normal human neutrophils, but not with lymphocytes, or unstimulated HL-60 cells. Furthermore, the presence of 20 nmol of FMLP inhibited the binding of five of the anti-receptor antibodies to whole PMN. These results suggest that the epitopes recognized by these five antibodies may possibly be involved in FMLP binding.

An IgM pan-T monoclonal antibody that blocks E-rosette formation.

An IgM monoclonal antibody directed against the T-cell E-rosette receptor was obtained by preparing a hybridoma against cells of a human T-cell leukemia line, HPB-ALL. The antibody, named EDN-34B1, reacts exclusively with cells of T-cell lineage, including those of three T-cell leukemia lines. It does not react with cells of B-cell lines, normal B-cells, or monocytes. EDN-34B1 recognizes a single polypeptide of approximately 50,000 molecular weight, is capable of blocking E-rosette formation, and its binding to the target cell can be specifically blocked by monoclonal antibodies 9.6 and OKT-11, both anti-E-receptor antibodies. EDN-34B1 is 100% cytotoxic against normal thymocytes and peripheral T-cells, thus enabling the routine removal of such cells from a mixed lymphocyte population, and kills a higher percentage of normal T-lymphocytes than Ab 9.6, even though immunofluorescence studies have shown that both antibodies bind to the same fraction of PBLs. This phenomenon may be due to the IgM nature of EDN-34B1. Addition of EDN-34B1 and complement to PBLs totally abrogates T-cell functions such as mitogen (PHA) stimulation and response in MLR, while addition of EDN-34B1 alone only affects MLR.

Fibrinogen-neutrophil interactions in response to fMLP and Porphyromonas gingivalis fimbrial peptides.

Porphyromonas gingivalis (P.g) is the primary bacterial agent in many forms of chronic periodontitis. Since polymorphonuclear leukocytes (PMNs) are first-line responders to P.g.- induced inflammation, and fibrinogen is important for in vivo PMN in this disease, we have studied the effect of N-formyl-methionyl-leucyl-phenylalanine (fMLP) (an inflammatory stimulus), P.g. fimbriae and fimbrial peptides (based on FimA, the main structural protein of P.g. fimbriae) on PMN-fibrinogen interactions. Freshly isolated human PMNs were allowed to react with FITC-Fibrinogen and various fimbrial peptides (denoted as FimA followed by amino acid number within whole FimA protein), and FITC-Fibrinogen binding was measured using flow cytometry. Freshly isolated neutrophils were also challenged with Fibrinogen and/or fimbrial peptides to measure IL-8 secretion using ELISA. Our studies show that fibrinogen binding to PMNs is enhanced (p < 0.01) in response to fMLP as well as fimbrial peptides (FimA 61-80) containing the motif LTTE (p < 0.01) in a dose dependent manner but not in response to peptides without that motif. We also observed that fMLP and FimA 61-80 have an additive effect on fibrinogen binding to PMNs (p < 0.05), and fMLP and FimA 171-185 significantly inhibit fMLP-induced fibrinogen binding (p < 0.01). To determine of the role of inflammatory cytokines, we examined IL-8 release from PMNs in response to combinations of P. gingivalis fimbriae, fMLP and fibrinogen. In all cases, IL-8 release increased in a dose-dependent manner (p < 0.05). fMLP-fibrinogen effect on IL-8 release from PMNs was synergistic while fimbriae-fibrinogen effect was additive. In summary, PMN priming by fimbrial peptides facilitates fibrinogen-PMN interaction and may increase inflammation.

The role of inflammatory and immunological mediators in periodontitis and cardiovascular disease.

Epidemiological studies have implicated periodontitis (PD) as a risk factor for development of cardiovascular disease (CVD). Persistent infections such as periodontitis induce inflammatory and immune responses which may contribute to coronary atherogenesis, and, in conjunction with other risk factors, may lead to coronary heart disease (CHD). In this review, mechanisms are described that may help explain the association between periodontal infections and CHD. Periodontal diseases are bacterial infections associated with bacteremia, inflammation, and a strong immune response, all of which may represent significant risk factors for the development of atherogenesis, CHD, and myocardial infarction (MI). Several mechanisms may participate in this association, including those induced by oral organisms, and those associated with host response factors. This review will focus on host factors. Oral pathogens and inflammatory mediators (such as interleukin [IL]-1 and tumor necrosis factor [TNF]-alpha) from periodontal lesions intermittently reach the bloodstream inducing systemic inflammatory reactants such as acute-phase proteins, and immune effectors including systemic antibodies to periodontal bacteria. This review will describe the potential role of various inflammatory as well as immunologic factors that may play a role in periodontitis as a possible risk factor for CHD.

Structural and functional characterization of the human formyl peptide receptor ligand-binding region.

The formyl peptide (N-formyl-1-methionyl-1-leucyl-1-phenylalanine [FMLP]) receptor is involved in the activation of neutrophils and their subsequent response to chemotactic N-formylated peptides. Recently, we found that the first extracellular loop closest to the N-terminal end of the FMLP receptor exhibited the strongest ligand binding compared with that shown by other extracellular regions. By constructing amino acid substitutional variants of this domain, we have determined that residues Arg-84 and Lys-85 on this loop play major roles in ligand-binding activity. Furthermore, random rearrangement of the residues of this receptor region demonstrated that the position of these charged amino acids did not affect their involvement in ligand binding, although their presence was essential for this binding to occur. We propose that the portion of the first N-terminal extracellular loop of the FMLP receptor containing residues Arg-84 and Lys-85 contributes significantly to the active site in ligand-receptor binding. We further propose that this binding is not dependent on defined structure but rather that these charged moieties may function as important "contacts" in receptor-ligand interactions.

Isolation and partial characterization of the formyl peptide receptor components on human neutrophils.

The receptor for formylated peptides such as FMLP has been reported to consist of glycoprotein components ranging from 24-95 kDa, and to exhibit both high and low affinity for ligand. Controversy exists on the molecular size and number of these components, and whether the different affinities represent distinct ligand binding sites. In this study, the receptor was found to be comprised of components, of 94, 68, and approximately 40 kDa molecular size. Competitive binding inhibition experiments showed that FMLP bound to the components in the following order from highest to lowest affinity: 68 kDa greater than approximately 40 kDa greater than 94 kDa. Our findings suggest that the FMLP receptor of human neutrophils contains at least three components, and that each component has a different affinity for FMLP.

Localization of ligand binding regions of the human formyl peptide receptor.

The formyl peptide receptor is involved in the activation of human neutrophils (PMN) and their subsequent response to chemotactic peptides such as FMLP. The normal FMLP receptor has been reported to contain both high and low affinity states and to consist of several glycoprotein components, ranging in size from 40-94 kDa. However, little is known about the functional domains of the receptor. In this study we have constructed synthetic peptides corresponding to different portions of the reported receptor structure, and have tested their involvement in ligand binding. One of these peptides, corresponding to the first extracellular loop of the N-terminus end of the molecule, has been shown to specifically inhibit FMLP binding to PMN membranes. Concomitantly, this peptide exhibited the strongest direct binding to the ligand. We propose that this portion of the FMLP receptor molecule is important in receptor-ligand interactions.

Subtle differences between human and rabbit neutrophil receptors shown by the secretagogue activity of constrained formyl peptides.

Stereochemically constrained extended beta-antiparallel and folded beta-turn analogs of the chemotactic agent N-formyl-Met-Leu-Phe-OH were tested for their ability to induce the release of beta-glucuronidase from human and rabbit neutrophils. Selected biologically active peptides were further examined for their capacity to inhibit the binding of f-Met-Leu-[3H]Phe to whole human neutrophils at 4 degrees C. The results suggest that Dpg2 analogs with the extended backbone are significantly more potent in human peripheral blood neutrophils than the folded beta-turn analogs. Surprisingly, in rabbit peritoneal neutrophils, the extended Dpg2 analog appears to be marginally less active than the flexible parent peptide and the folded Ac6c2 analog. In human neutrophils, the secretagogue activity increases in the following order with alteration in the C-terminal functions: -CONH2 < -COOMe < -COOH << -COOBzl. However, this order of potency differs from that observed for the rabbit formyl peptide receptor (-COOH < -COOMe < -CONH2 << -COOBzl). In human neutrophils, the peptides' ability to compete for the receptor binding site of f-Met-Leu-[3H]Phe correlates well with their secretagogue potency. The results provide convincing evidence for the existence of subtle differences between human peripheral blood neutrophils and rabbit peritoneal neutrophils with regard to ligand-receptor interactions of constrained chemotactic peptides. What is new and novel in this report is that constrained peptides can distinguish between the rabbit and human chemotactic peptide receptors which have so far been believed to have similar response to secretagogue agents. The data emphasize that directly relating the secretagogue activity observed in rabbit neutrophils to that observed in human neutrophils may not be unequivocal.

Interleukin 8, neutrophil-activating peptide-2 and GRO-alpha bind to and elicit cell activation via specific and different amino acid residues of CXCR2.

The objective of this investigation was to determine the amino acid residues of the human neutrophil CXC chemokine receptor-2 (CXCR2) that are critical for binding the ligands interleukin 8 (IL-8), neutrophil-activating peptide-2 (NAP-2), and growth-related protein alpha (GROalpha) and critical for receptor-mediated signal transduction. Charged residues of the amino terminus and the first extracellular loop of CXCR2 were targeted for point mutagenesis studies. Seven separate CXCR2 mutants (Glu7, Asp9, Glu12, Asp13, Lys108, Asn110, and Lys120, all to Ala) were generated. Based on the Scatchard analysis of radioligand binding studies, the following amino acids were deemed critical for ligand binding: (i) Asp9, Glu12, Lys108, and Lys120 for IL-8 and (ii) Glu7, Asp9, and Glu12 for GROalpha. Point mutations in the amino terminus domain (Asp9 and Glu12) and the first extracellular loop (Lys108, Asn110, and Lys120) of CXCR2 reduced cell activation to all three ligands as measured by changes in intracellular calcium concentration. In conclusion, high-affinity binding of IL-8, NAP-2, and GROalpha to CXCR2 involves interaction with specific and different amino acid residues of CXCR2. Furthermore, we propose that the CXCR2 amino acid residues required for cell activation are not necessarily the same residues required for ligand binding.

Human formyl peptide receptor function role of conserved and nonconserved charged residues.

In this study, we investigated the role of charged residues in ligand binding interactions of f-Met-Leu-Phe receptors (FPR). Charged residues of FPR, both conserved and nonconserved, which are located close to the membrane interface were mutated to alanine to determine their role in ligand binding. The mutated residues belonged to specific domains of FPR which have previously been implicated in FPR ligand binding interactions. We demonstrate that nonconserved charged residues such as Arg84, Lys85, Arg205 and Asp284 and conserved charge residue Arg163 seem to play a role in ligand binding. However, alteration of nonconserved charged residue Asp106 did not have any effect. In conclusion, specific charged residues of FPR, both conserved nonconserved, may contribute to FPR function either directly or indirectly.

Quantitative approach for detection and characterization of formyl peptide receptor in solution using a photoaffinity ligand.

In this paper we describe an assay method for the rapid detection and quantitation of human neutrophil FMLP (N-formyl-methionyl-leucyl-phenylalanine) receptor molecules. Although different assay methods are available to detect the receptor, none are rapid and at the same time allow quantitative detection of the binding affinity of the receptor molecule in solution. In our modified method, following a binding reaction using photoaffinity ligand, the amount of labeled ligand bound to the receptor is separated from the unbound one, thereby determining the binding affinity of the receptor protein. This simple procedure not only makes it possible to detect the recombinant FMLP receptor protein very rapidly, but also provides quantitative assessment of binding. This technique therefore allows a partial characterization (identification, determination of size and assessment of binding affinity) of receptor molecule in solution in less than 24 hours.

Identification and characterization of human immunoglobulin G Fc receptors of Fusobacterium nucleatum.

Several human pathogens express components which can bind to the Fc portion of immunoglobulins. This study was undertaken to characterize the human immunoglobulin G (IgG) Fc-binding activity of Fusobacterium nucleatum, a suspected pathogen involved in periodontal diseases. Fc-binding activity was detected using whole-cell, cell envelope and outer membrane fractions, and it was found to be associated with polypeptides of 40 kDa and 42 kDa, respectively. Amino terminal sequencing of these components revealed them to be homologous to the bacterial porin encoded by fomA gene. Further sequencing of internal peptide fragments obtained by CNBr cleavage suggested that these two proteins are probably isoforms. In summary, we show that a porin-like protein on the surface of F. nucleatum can bind the Fc fragment of the human immunoglobulin G, and this protein may act as a virulence factor to facilitate this bacterium in evading host immune surveillance system.